PI3Ks are a family of lipid kinases that catalyze the phosphorylation of the membrane lipid phosphatidylinositol (PI) on the 3′-OH of the inositol ring to produce PI 3-phosphate [PI(3)P, PIP], PI 3,4-bisphosphate [PI(3,4)P2, PIP2] and PI 3,4,5-trisphosphate [PI(3,4,5)P3, PIP3]. PI(3,4)P2 and PI(3,4,5)P3 act as recruitment sites for various intracellular signaling proteins, which in turn form signaling complexes to relay extracellular signals to the cytoplasmic face of the plasma membrane.
Eight mammalian PI3Ks have been identified so far, including four class I PI3Ks. Class Ia includes PI3Kα, PI3Kβ and PI3Kδ. All of the class Ia enzymes are heterodimeric complexes comprising a catalytic subunit (p110α, p110β or p110δ) associated with an SH2 domain-containing p85 adapter subunit. Class Ia PI3Ks are activated through tyrosine kinase signaling and are involved in cell proliferation and survival. PI3Kα and PI3Kβ have also been implicated in tumorigenesis in a variety of human cancers. Thus, pharmacological inhibitors of PI3Kα and PI3Kβ are useful for treating various types of cancer.
PI3Kγ, the only member of the Class Ib PI3Ks, consists of a catalytic subunit p110γ, which is associated with a p101 regulatory subunit. PI3Kγ is regulated by G protein-coupled receptors (GPCRs) via association with βγ subunits of heterotrimeric G proteins. PI3Kγ is expressed primarily in hematopoietic cells and cardiomyocytes and is involved in inflammation and mast cell function. Thus, pharmacological inhibitors of PI3Kγ are useful for treating a variety of inflammatory diseases, allergies and cardiovascular diseases.
Although a number of PI3K inhibitors have been developed, there is a need for additional compounds to inhibit PI3Ks for treating various disorders and diseases, such as autoimmune diseases, inflammatory diseases, cancer, allergic diseases, asthma, and respiratory diseases. Accordingly, it would be desirable to develop additional compounds that are useful as inhibitors of PI3K.